Drilling method and apparatus



March 29, 1960 H. mm; 2,930,586 A DRILLING METHOD AND APPARATUS 4Sheets-Sheet 1 Filed July 25, 1955 March 29, 1960 R. H. LONG 2,930,586

DRILLING METHOD AND APPARATUS Filed July 25, 1955 4 Sheets-Sheet 2lllmlln. "In.

x V hi v v v ATTORA/EKJ' March 29, 1960 R. H. LONG 2,930,536

DRILLING METHOD AND APPARATUS Filed July 25, 1955 4 Sheets-Sheet 3 lR/c/7a/a /7 [0/7 INVENTOR.

///%01/ 24 A770 A/EKS March 29, 1960 R; H. LONG DRILLING METHOD ANDAPPARATUS 4 Sheets-Sheet 4 Filed July 25, 1955 fP/CfiQ/Q b. [anyINVENTOR.

United States Patent G 2,930,586 DRILLING METHOD AND APPARATUS RichardH. Long, Houston, Tex. Application July 25, 1955, Serial No. 524,069 4Claims. (Cl. 2251.8)

This invention relates to a drilling method and apparatus, and moreparticularly to a method and apparatus for drilling a smooth wallstraight hole in the ground of a size which may be used for a mineshaft.

In some types of mine operations, such as uranium mining, the depositsare not in continuous veins which may be worked for long periods oftime, but tend to be found more in deposits which support a year or twoof operation and then the deposit must be abandoned and operationsshifted to a new location. As uranium is frequently found a considerabledistance under the surface of the earth, the cost of sinking a pluralityof mine shafts to work an area is substantial and the industry would beconsiderably benefited if this cost could be reduced.

The method previously used to sink such shafts involves manual diggingthrough soft formations and blasting to penetrate hard formations. Spoilis removed by an elevator in the shaft. In hard formations the usualpractice is to drill shot holes in the formation and blast. Shot holesare spaced at two foot intervals in the bottom of the hole immediatelyadjacent the wall of the hole and at two foot intervals over the bottomof the hole. Explosives are then placed in the holes adjacent the wallof the shaft and detonated. Men are then sent into the shaft to removeloose rock. Explosives are then placed in the remaining shot holes anddetonated. Rock loosened by this blast is removed and the operationrepeated. As men cannot remain in the shaft during detonation of theexplosives, two trips to the surface are required to blast each verticalincrement of the shaft. From the above it can be seen that work would bemuch faster and more economical if a continuous drilling method andapparatus such as used for could be devised to sink such shafts.

Rotary drilling methods and apparatus heretofore in use in drillingwater wells, oil and gas wells, etc., however, are not usable. While therotary'drilling industry has known a method for drilling a smalldiameter pilot or rat hole straight down into the earth, the industryhas not heretofore developed a method and apparatus for drilling a largediameter hole straight down into the earth. In a small hole the area ofthe bottom of the hole is relatively small and the hole can be deepenedwith but relatively small weight on the bit if the hole is drilledslowly. However, when the hole is of relatively large diameter, the areaof the bottom of the hole is so large that the bit must by provided withthousands of pounds of extra weight to provide the downward force on thebit formation. The conventional way of providing such weight is topermit some of the weight of the drill string to be exerted upon thebit. The drill pipe is always smaller than the hole being drilled andthe slenderness ratio of the pipe relative to the weight of the stringis such that the string will bow adjacent the bit and in many instanceswill assume the form of a corkscrew while being rotated. As a result ofthe bowed, corkoil, gas, and water wells necessary to force it topenetrate the ing the shaft shown in Fig.

screwed drill string, the bit tends to drill at an angle to the verticaland to drill a corkscrew hole.

A mine shaft must be vertical to permit'its use as an elevator shaft toraise and lower men and equipment, and to remove ore from the earth. Italso must be vertical and smooth to prevent cave-ins if the wall is notto be timbered, or cased. A rough wall is undesirable as protrusionsfrom the wall will tend to break off and fall into the hole onto theelevator and men working below.

It is an object of this invention to provide a method and apparatus fordrilling a mine shaft utilizing bits operated from the surface.

Another object is to provide a method and apparatus of sinking a mineshaft utilizing at least in part rotary bits in which the resultantshaft is smooth walled and vertical and in many instances need not betimbered or cased.

Another object of this invention is to provide a drilling method andapparatus utilizing at least in part rotary bits for drilling a straightsmooth wall hole into the ground of a diameter suitable for use as amine shaft.

Another object is to provide a method for rotary drilling a largediameter hole with a large diameter bit in which the weight for drivingthe bit into the formation is applied to the bit in a manner which willnot cause the bit to depart from a vertical digging axis.

Another object is to provide a method and apparatus for operating a holeopener bit in a pilot hole in which the rotational axisof the bit ismaintained coincident with the axis of the pilot hole.

Another object is to provide a method for drilling a large diameter holesuitable for use as a mine shaft in which the hole is drilled withsuccessively larger bits and after the initial pilot hole has beendrilled straight down into the ground, rotary bits are utilized and thewall of the hole made by the preceding bit is utilized to maintain therotational axis of the rotary bit coincident with the axis of the holemade by the preceding bit.

Another object is to provide a method of enlarging a pilot hole using arotary bit in which the drill string is under tension during drillingwith the rotary bit to prevent the weight of the drill string fromtending to tip the bit from its vertical axis of rotation.

Another object is to provide apparatus for removing cuttings from alarge diameter hole in which at least the larger cuttings are removedthrough a small diameter conduit by fluid introduced into the holeinside of the drill string.

Another object is to ing cuttings from a hole opener bit from the holeby catching the cuttings below'or above the cutting face of the bit andconveying them into an upwardly flowing fluid stream such as air, gas,water, mud, etc., which conveys the entrained cuttings to the surface.

Other objects, features and advantages of this invention will beapparent from a consideration of the drawings, the written specificationand the appended claims.

In the drawings wherein there is shown by way of illustration a mineshaft drilled into the ground utilizing this invention and wherein thereis shown one form of apparatus for drilling said shaft, and wherein likereference numerals indicate like parts:

Fig. l is a view partially in vertical cross section and partially inelevation of a portion of a mine served by a shaft drilled in accordancewith this invention and of the surface handling equipment for the mine;

Fig. 2 is a view in vertical section through a pilot hole showing invertical elevation a form of apparatus used in sinking the pilot holewhich is the provide an apparatus for remov-.

first stage of sink- Fig. 3 is a view in vertical section through thepilot hole showing in elevation a hole opener bit and stabilizer used toream out the pilot hole to a larger diameter;

Fig. 4 is a view in vertical section through the hole cut by the holeopener bit shown in Fig. 3, and showing. in elevation a still largerhole opener bit utilized in' reaming out the hole to a still largerdiameter and having parts broken away to illustrate the manner in whichcuttings are conveyed to the surface; p a

Fig. 5 is a view in elevation of a plug usable with the Fig.4 and Fig. 6apparatus; and

Fig. 6 is a view partially in vertical cross section and partially invertical elevation of a basket positioned above the hole opener bit. a

Referring now to Fig. 1, there is shown schematically a typical mineemploying a vertical shaft indicated generally at it to work thehorizontal shaft 11 extending therefrom. Ore taken from the horizontalshaft is loaded into an elevator 12 by means of a hopper arrangementindicated generally at 13 and raised to the surface through thecable-handling apparatus indicated generally at 14 and by a suitabledraw works not shown. With the elevator in its uppermost position theore is transferred to a waiting car 15 through a suitable hopperarrangement indicated generally at 16. The elevator is provided with acage 17 to transport men to and from the shaft. 'It will be apparentthat for the elevator to be operable the shaft 16 must be vertical toprevent the elevator from dragging on the walls. The walls must besmooth and straight to prevent possible cave-ins and breakolfs of roughedges of the Wall which would fall into the bottom of the shaft andpossibly injure men working in the mine.

The method of rotary drilling shaft comprises, first, drilling astraight small pilot or rat hole to the desired depth and then reamingoutthis pilot hole to the desired size whilemai-ntaining the rotationalaxis of the bit concentric with the bore of the pilot hole to providethe smooth wall straight shaft 10.

In drilling the pilot hole a small diameter bit of conventional typeused in drilling oil and gas wells and a conventional rig and rotarymeans for rotating the drill stem are employed. A drill collar isinterposed in the string immediately above the bit and provided withspaced rollers or reamers arranged circumferentially about the collarsand spaced in groups along the" collar to provide a stabilizer to holdthe bit on a straight course. The hole is drilled with just enough"weight on the bit to provide the force necessary for the bit to cutinto the bottom of the hole. At frequent intervals an'inclinomcut.

eter is employed to check thed'rill hole inclination. By

using the stabilizer and permitting only a small downwardweight tobeexerted onthe bit, the hole should remain vertical. If the inclinometerindicates, however, that the bit has turned and that there is a dog legin the hole, then the bit must be withdrawn and the rig shifted to a newlocation and the drilling operation recommenced as the pilot holemust bevertical. Drilling a' vertical pilot hole is not too difficult when thestabilizer isemployed above the drill and the driller carefully main--tains the proper weight on the bit.

After the pilot hole-has been completed, a hole opener bit is employedto ream-out the pilot hole to alarger diameter. A weight is dependedfrom the hole opener bit and extends into the pilot hole below the bitto force the hole opener bit into the formation. Preferably, the weightis provided by a stabilizer engageable with the wall of the pilot holeto maintain the bit on the proper axis of rotation. The stabilizer usedin drilling the pilot holeis' ofa proper size and is preferably used forthis service, the stabilizer and the bit utilized in drilling the pilothole being depended from the hole opener bit so that they precede thehole opener bit into the pilot hole.

Dueto-the large weight of drill collars, thestabilizer will provide theweight for driving the hole opener bit down-- ward to penetrate theformation. If additional weight is desired then the stabilizer islengthened with additional drill collars to provide such weight. Thepilot hole bit is left on the bottom of the stabilizer to make certainthat the hole below the hole opener bit is clear. Ordinarily the pilothole bit will not function during the operation of the hole opener bit.It is made up in the string just in case it may be needed to open up thepilot hole or to mulch cuttings in the bottom of the hole so that theymay be removed.

In the operation of the hole opener bit a tension is taken on the drillstring from which the hole opener bit depends so that the weight of thedrill string will not rest upon the hole opener bit, thus the drillstring being in tension will not tend to corkscrew or to bow as is thecase when the weight of the string is allowed to rest in part upon thebit. It is pointed out that if the weight of the drill string werepermitted to rest on the hole opener bit and tended to cock itsrotational axis relative to the pilot hole central axis there would be atendency to snap off the stabilizer and, hence, the driller should payclose attention to his weight indicator and maintain the string under atension which will prevent the weight of the string resting upon thehole opener bit. As the pilot hole is vertical, there is no need tocheck the hole opener bit as the stabilizer will hold it on course androtary drilling to ream out the pilot hole may be continued usingconventional drilling methods until the hole is reamed to its bottom.

Due to the increased area of contact between the cutting face of the bitand the bottom of the hole as the diameter of the hole increases, itwill be appreciated that it will be desirable to use successively, holeopener bits of successively larger diameters to open the hole to thedesired diameter. In each instance of use of the hole opener bit,however, there is depended from the bit a stabilizer engageable with thewall of thehole previously For instance, after the first hole opener bithas been run into the hole and withdrawn, then a larger hole opener bitwould be used in conjunction with a stabilizer having means engageablewith the wall of the hole. PreferablyQthe means for engaging the wallare rollers or reamers mounted with their outermost points in a circleequal to the diameter of the hole just cut, but it will be appreciatedthat they might be mounted in a slightly smaller circle and stillfunction to maintain the hole opener bit rotational axis substantiallycoaxial with the axis of the hole being reamed. This process iscontinued until the hole is reamed to the desired diameter after whichthe surface equipment is removed and the surface equipment illustratedin Fig. l erected over the hole. Between runs a long cylinder of butslightly less diameter than the hole may be runto insure that the holeis straight before beginningthe' next stage of drilling. The horizontalshaft isthen dug in the usual manner.

Due'to' the fact thatthe hole opener bit was held on a vertical axisofrotation the wall of the shaft will be smooth and straight and noproblem of cave-in or breakoif of protruding material will be present inhardformations such as rock. However, it may be necessary to casecavities' or soft formations such as water sands.

'Referring now to Figs. 2, 3 and 4 and to the tools used in drillingshaft 10, reference is first made to Fig. 2 which stabilizer indicatedgenerally at 21 which engages the wall of hole 18 to maintain thestabilizer centered in hole 18. The stabilizer 21 is made up of aplurality of drill collars 22 which are threaded into a tool joint 23 onthe -bottom'of drill string 20. Drill collars are chosen for the'bo'dyof the stabilizer due to their great strength and weiglitasit is desiredto localize" the weight o'ntlie pilot hole bit as close to the bit aspossible and to have this weight controlled by the stabilizer. Thus, ifa 500- 1b. downward force is needed to operate the pilot hole bitindicated generally at 24 and the stabilizer 21 provides such 500-lb.force, then the drill string 20 may be in tension and the downwardthrust of the 500-lb. force held exactly vertical by the stabilizer.

The stabilizer 21 is provided with groups of vertically spacedhole-engaging means such as rollers or reamers 25 groupedcircumferentially aboutthe stabilizer at its upper end, rollers orreamers 26 grouped circumferentially about the stabilizer at anintermediate point, and rollers or reamers 27 grouped circumferentiallyabout the stabilizer adjacent its bottom end. These rollers whenemployed in spaced groups preferably include three or more rollersspaced equidistant about the stabilizer at each level. In the formillustrated in Fig. 2, four rollers equally spaced circumferentiallyabout the stabilizer are employed in each vertically spaced group.

Preferably, the rollers 25, 26 and 27 are mounted on axes extendinggenerally axially of the stabilizer and lying within a single circlewhich is concentric with the rotational axis of the stabilizer and pilothole bit 24 which is secured to the bottom end of stabilizer 21. Theradially outermost points of each of rollers 25, 26 and 27 prescribe acircle which is of equal diameter with the diameteriof a hole dug by bit24. These rollers will tend to smooth out any irregularities left in thewall of the pilot hole by the bit 24 while holding bit 24 on a straightpath.

The apparatus of Fig. 2 is operated in the conventional manner with justsufiicient weight on bit 24 to drive it into the formation until thedesired depth of the pilot hole has been reached. At frequent intervals,an inclinometer is utilized in the conventional manner to check theangle of inclination of the pilot hole 18 and if the hole departs fromthe vertical, the string is withdrawn and moved to a new location wherea new pilot hole is started as the pilot hole must be vertical.

After the pilot hole has been completed to the desired depth, thestabilizer 21 is broken out of the drill string 20 and a hole opener bitindicated generally at 28 (Fig. 3) is aflixed to the drill string. Asuitable stabilizer is depended or suspended from the hole opener bit toguide the hole opener bit and to provide the weight for forcing the bitinto the formation. To avoid any tendency of the bit to tilt and leavethe pilot hole due to the center of gravity of the weight for forcingthe bit into the formation being above the cutting face 29 of the bit,substantially all of the weight on the hole opener bit 28 should besupplied from below the cutting face 29 of the bit. The stabilizershould be provided with surfaces which will engage the wall of hole 18below the hole opener bit 28 if the bit attempts to depart from arotational axis coincident with the central axis of pilot hole 18. Asthe stabilizer 21 will admirably perform both of these functions, it ispreferably employed. 4 If it is desired to add more weight than thestabilizer 21 as used in drilling a pilot hole will provide, thenadditional drill collars are made, up in the stabilizer to provide suchadditional weight. As the wall-engaging rollers 25, 26 and 27 of thestabilizer are arranged to run in a circle which is equal to thediameter of pilot hole 18, these rollers will engage the wall of hole 18at vertically spaced points below the hole opener bit 28 and willmaintain the rotational axis of the hole opener bit coincident with theaxis of pilot hole 18.,

In operation of the hole opener bit of Fig. 3, the drill string 20should be maintained under tension so that the weight of the string willnot be exerted upon the hole opener bit 28 and tend to tilt it from avertical axis. It may be possible that a small amount of the weight ofthe drill string might be exerted upon the hole opener bit 28 withouttipping the bit from its vertical rotational axis due to the action ofstabilizer 21, but it is preferred that all of theweight be suppliedbelow the cutting face of the hole opener bit. 1

'The hole opener bit is operated in the conventional manner withcuttings returned to the surface entrained in a fluid introduced intothe hole through the drill string and returned to the surface in theannular space between the drill string and the bore of the enlarged hole30. Fluid such as air,' gas, liquid or mud passing from the drill stringinto pilot hole 18 from the outlets in bit 24 will return up pilot hole'18 and prevent cuttings from falling into the pilot hole 18. Anycuttings which fall past the stabilizer will be mulche'd by bit 24 whenit reaches the bottom of the pilot hole and carried to the surface byair from outlets in hit 24. In the event it is found expensive ordifiicult to remove cuttings from the hole in the conventional manner,then a special method of handling the cuttings to be described presentlymay be employed.

After the hole opener bit 28 has been withdrawn, it will probably bedesired to ream out hole 30 to a still larger diameter and for thispurpose a still larger hole opener bit indicated generally at 31 in Fig.4 may be'employed. Hole opener bit 31 is depended from drill string 20in the same manner as was hole opener bit 28 and a stabilizer indicatedgenerally at 32 is depended from hole opener bit 31 in the same manneras stabilizer 21 was depended from hole opener bit 28 in the Fig. 3apparatus. As the rat hole was enlarged to form hole 30 by the holeopener bit 28, the stabilizer 32 must be of a larger diameter, that is,a diameter which will engage the wall of hole 30 if bit 31 leaves anaxis of rotation coincident with the central axis of hole 30. Thisstabilizer will again provide the weight for forcing the bit into theformation.

As indicated above the stabilizer does not necessarily require rollerswhich run in a circle of equal diameter with the hole, nor are rollersnecessary. Thus, the stabilizer 32 is cylindrical and has a diameterwhich is slightly less than t he diameter of hole 30 so that the outerperipheral surface 33 of stabilizer 32 will not bind in the hole, yetwill engage the wall of hole 30 when necessary to maintain therotational axis of bit 31 coaxial with the central axis of hole 30.Preferably, the stabilizer 32 is of a length which will cause it toengage the hole upon slight departure of bit 31 from the properrotational axis. While the stabilizer is indicated to be rigidly securedto the bit, it may be secured to the bit in any other desired manner aswill be understood by those skilled in the art.

In operating the hole opener bit 31, the entire weight for driving thecutting face of the bit into the formation is preferably provided by thestabilizer 32. The bit is operated in the same manner as was hole openerbit 28 to Team out hole 30 to form shaft 10. As the wall of shaft 10 isvertical and smooth, it will not be necessary to timber or case the wallto prevent cave-ins and breaking off of rough edges unless it is desiredto do so in soft formations.

Referring now to the means for returning cuttings to the surface shownin Fig. 4, it will be noted that the cuttings are returned to thesurface within drill string 20 instead of within the annular spacebetween the drill string and thejwall of hole 19. Entraining cuttingswithin a vertical stream of air or gas requires terrific air velocityand it is easier to provide this velocity within a small diameter pipe,such as drill string 20, than in the large diameter hole 10.

In order to catch the cuttings as they fall into hole 30, there isprovided an annular basket 36 arranged concentric with and carried bystabilizer 32 immediately below bit 31. The upper end of stabilizer 32has a reduced diameter portion 35 to provide an annular space betweenthe stabilizer and basket wall into which cuttings may fall. The basket36 has an outer diameter but slight 1y, smaller than the diameter ofhole 30 to prevent cutu 7 V tihgs from falling into the space betweenthe basket and hole 30. The lower end of the basket has a constantlyreducing diameter portion 37 which necksabout stabilizer 32 in the formof a funnel so that cuttings fromdrill 31 will be directed to lateralpassageways 38 and 39 which conduct cuttings from basket 36 to a jetmixer 40 within the Stabilizer bore 50. Mixer 40 is a generally tubularmember extending coaxially with stabilizer bore 50 and has a jet inlet41 in its lower end. Its upper end terminates in an outwardly beveledseat for receiving an inner string of tubing 42 in the drill string toconvey cuttings from the mixer to the surface. Lateral passages 38 and39 conduct cuttings into the mixer immediately above the jet where theyare mixed in the fluid such as. air or gas passing through the jet andccnveyed to the surface. Tubing 42 extends upwardly from the basketthrough the stabilizer and bit and within drill string 20 to. thesurface. Where this arrangement us used, a plug 43 may be positionedwithin the stabilizer 32 immediately below the bottom end of the innerstring of tubing 42 so that air introduced into the drill string willtravel downwardly in the annular space betweenthe inner string of tubing42 and drill string 20 through a bore. 44 in bit 31, and into bore 50 instabilizer 32', through holes 40a into chamber 40b and thence upwardlythrough jet 41 to entrain cuttings and then up the inner string oftubing 42. If desired, an annular sleeve shown at 45 may be carried byinner string 42 in a position to overlie passageways leading to thefluid outlets in the bit31 so that substantially all of the fluid in thedrill string will be directed to jet 41. When the sleeve is used, itwill be appreciated that after the basket 36 has been cleaned out theinner string 42 will be pulled and a plug 47, shown in Fig. 5, seated inmixer 40 with a wire line. The bit will then be operated until basket 36is filled with cuttings at which time plug 47 will be pulled, innerstring 42 reinserted, and the basket 36 again cleaned out. Duringdrilling operations fluid may be continuously circulated in theconventional manner in the hole and some or the lighter cuttings will bebrought to the surface by such fluid and only the heavier cuttings willfall into basket 36.

in some instances it may be desirable to employ a basket above the holeopener bit. For instance, if the basket method is to be used when thefirst hole opener bit 28 is run, .the pilot hole 18 is rather small andthe basket would desirably be placed above the bit as shown in Pig. 6.While of a diiierent size, basket 48 is identical inconstruction withbasket 36. Mixer 49 is identical in construction and function with mixer40. During drilling operations cuttings are. picked up by fluiddelivered to the bit in the conventional manner and carried up the hole.W'hile light cuttings will be carried to the surfac'e, some of the heavycuttings will be carried up a short distance and then tend to fallbackif a light fluid such as air or gas is used to wash the hole. Byposithat an er at tioning basket 48 above the bit and providingsufiicient fluid velocity, heavy cuttings will be lifted above thebasket and fall back into the basket. Fluid will be forced throughholes4% of mixer 49 and on down into the bit 24. However, due to the pumppressure on the.

downflowing fiuid and the lack of such pressure in tubing 42, part ofthe fluid flowing down through holes 49a into the space 49!) will flowup through the jet 490 into tubing 42. These heavy cuttings from thebasket 48 will then be fed into mixer 49and be conducted to the surface.If desired, the plug 47 may be seated in mixer 49' during drilling andthen removed and the basket cleaned as in the case of the basket belowthe hole 7 From the above it will be seen that all of the objects ofthis application have been accomplished. There has been provideda methodand an apparatus for rotary drilling a large diameter hole usable as amine shaft. The hole is vertical so that an elevator may move freelywithin the shaft andthe Wall ofthe' hole issmo'oth so is contemplated Vsssssss ca e-his. and breaking off of rough edges is, greatly minimized.There has been provided both a method and a suitable apparatus fordrilling asrnooth wall straighthole as well as a means for returning cutto the surface in the event circulation in the normal manner is notsatisfactory in removing the cuttings.

It will be understood that while this invention has been illustrated anddescribed in sinking amine shaft, it is usable in sinking a verticalhole into the ground for any purpose and may find particular applicationin drilling large diameter holes for the production of oil and gas wherethe drilling contract requires that the hole he held within narrowlimitsfrom the vertical or where a straight hole would be advantageous forworkover operations or .the like. This is contemplated by and isincluded within the scope of many of the claims. 7 I

From the foregoing it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the method and apparatus.

Itwill be understood that certain features and subcombinations are ofutility and may be employed without.

reference to other features and subcombinations. This by and is withinthe scope of the claims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanyingdrawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. The method of rotary drilling a hole having a straight, smooth walland closed bottom comprising the steps of drilling a relatively smalldiameter pilot hole straight down into the earth from the surface to thedesired depth, rotary reaming the pilot hole to a larger diameter with arotary hole opener bit rotated by a drill string under tension,suspending below and from the bit in the pilot hole during said reaminga weight sufficierit in mass to provide the entire necessary downwardcutting force on the bit, and exerting on the upper end of said drillstring during drilling a lifting force in excess of the total weightof'the drill string above the hole opener bit, but less than theaggregate weight of the drill string, the bit and the weight suspendedbelow the bit, whereby the entire drill string will be maintained undertension during drilling, and the entire drilling force will be exertedon the bit from below the bit.

2. The method of claim 1 including in the reaming step repeated reamingswith successively larger hole opening bits, suspending below and fromeach hole opening bit in the hole below the bit a weight sufficient inmass to provide substantially the entire necessary downward cuttingforce on that bit, and exerting on the upper end of said drill stringduring drilling with each bit a lifting force in excess of the totalweight of the drill string above that bit, but less than the aggregateweight of the drill string, the bit and the weight suspended below thebit. 7 d d 3. In combination, a drilling apparatus comprising a holeopener. bit carried .by a drill string having a central boretherethrough, a stabilizer depending from the bit and engageable. withthe wall of a pilot hole to maintain the rotational axis of the bitcoincident with the central axis of the pilot hole, a basket carried bythe drill string and positioned to catch cuttings from the bit, a jetfor introducing a pressure fluid upwardly into the drill string, andmeans for admitting cuttings from the basket into the drill string at apoint adjacent the jet outlet, whereby the pressure fluid will conveythe cuttings up the drill string.

4. A drilling apparatus in accordance with claim 3 in which there is aninner string of pipe within the drill string and forming an annularpassage therewith, the

9 into the inner string of pipe, the means for admitting cuttings fromthe basket into the drill string admits them into the inner stringadjacent the jet outlet, and the jet intake is connected to the annularpassage within the drill string ouside the inner pipe to receivepressure fluid therefrom.

References Cited in the file of this patent UNITED STATES PATENTS1,525,235 Hansen Feb. 3, 1925 1,547,461 Steele July 28, 1925 1,844,371Santiago Feb. 9, 1932 2,141,111 Mitchell Dec. 20, 1938 2,203,998 OGradyJune 11, 1940 2,208,530 Thompson July 16, 1940 10 2,281,614 Ogran May 51942 2,301,617 Cox et a1. Nov. 10, 1942 2,585,369 Caruthers Feb. 12,1952 2,634,101 Sloan Apr. 7, 1953 2,657,907 Cochran et al Nov. 3, 19532,688,871 Lubinski Sept. 14, 1954 2,703,698 Westerman Mar. 8, 19552,746,719 Seligman May 22, 1956 2,766,013 Hertzke Oct. 9, 1956 FOREIGNPATENTS 505,302 Belgium Sept. 15, 1951 OTHER REFERENCES New Eastco,"World Oil Magazine, February 15,

1955, page 119.

